1. Field of the Invention
The present invention relates to an image reading apparatus, and more particularly, to the one for opening and closing an original cover by a drive device.
2. Description of the Related Art
In general, an image reading apparatus mounted on an image forming apparatus such as a copy machine or a facsimile machine includes an original cover openable and closable with respect to an original stand on which an original is placed to be read.
When the image reading apparatus reads the original as a sheet, the original cover carries out a function to press the original placed on the original stand from above to prevent the original from being displaced, or a function to reflect a light from an exposure mechanism provided inside the apparatus main body so as to allow reading an excellent image.
In such an image reading apparatus, after the original cover is manually opened and an original is placed on the original stand, reading is performed in a state in which the original cover is closed, and after completion of reading, the original cover is manually opened again and the original is removed from the original stand.
Furthermore, in addition to the original cover arranged to be opened and closed manually as described above, there is an image reading apparatus having an original cover including an automatic original feeder conveying an original onto the original stand. However, the original cover including such an automatic original feeder requires a relatively large force for opening and closing the original cover because it is heavier as compared with an original cover without an automatic original feeder.
On the other hand, as with an invention described in Japanese Patent Application Laid-Open No. S61-256341, there is proposed an image reading apparatus in which an opening and closing drive portion, such as a motor for opening and closing the original cover with respect to the original stand, is provided in a hinge portion. This saves the trouble of opening and closing the original cover manually at the start of a copying operation and at the end of the copying operation, and prevents the original cover from being left unclosed and the original from being left.
When the original cover equipped with the opening and closing drive portion as described in Japanese Patent Application Laid-Open No. S61-256341 includes the automatic original feeder as mentioned above, the opening and closing drive portion must perform opening and closing drives in a state of supporting an entire load including the automatic original feeder. When the original cover having such a weight, for example, is driven so as to be opened and closed by one motor, heat or noise is likely to be generated because a load applied to the motor increases excessively. Accordingly, a problem arises that in order to obtain a torque suitable for opening and closing the original cover having the above-mentioned weight, a high-output motor with relatively large outer shape is required.
To solve the problem as above, it is conceivable that the motor as the opening and closing drive portion of the original cover is arranged at each of a plurality of locations of the original cover rather than one location.
For example, there is an original cover pivotally supported by the hinge portions at two locations, and in the case of the original cover like this, a motor for opening and closing the original cover is arranged at each hinge portion. However, in the case of an original cover including the automatic original feeder, each motor is not equal in rotary movement because a load applied to each motor is not uniform since a load distribution of the automatic original feeder is not uniform with respect to a profile of the original cover.
That is, when these two motors are equal in torque setting, although a motor arranged at a region side of the original cover relatively light in weight is likely to rotate faster than a motor arranged at a region side relatively heavy in weight, the former motor is restrained by the movement of the latter motor. When the movements restraining each other are repeated, the original cover becomes unstable in opening and closing actions, for example, the opening and closing actions are damaged in high quality feeling by accepting the opening and closing actions with yawing.
Furthermore, when the unstable opening and closing actions mentioned above are repeated, the original cover is twisted, and a component of the automatic original feeder may cause displacement or damage, generating a possibility to be influenced in a conveying performance of the original or a geometrical characteristic of the read image.